1. Field of the Invention
The present invention relates to a membrane filter system including a membrane filter for use particularly in bacteriological examination and cultivation.
2. Description of the Prior Art
One of typical methods for bacteriological examination is referred to as a HGMF (hydrophobic grid membrane filter) method wherein sample solution is caused to pass through a membrane filter of biologically inactive material such as PES polyethersulfone and PVDF (polyvinylidene difluoride) so that microorganism or bacteria contained in the sample solution is caught by the membrane filter.
Some different systems have been proposed to conduct the bacteriological examination in accordance with the HGMF method. One system comprises a funnel and a storage bottle, both made of glass material, which are connected to each other by a cylindrical coupler including a membrane filter. With this system, a predetermined quantity of the sample solution poured into the funnel will flow down into the storage bottle, during which microorganism contained in the sample solution is caught by the membrane filter.
Another example to be used for the HGMF filtration system comprises a plurality of funnels, each provided with a membrane filter at the bottom thereof and connected to a manifold. The manifolds are all connected to a main pipe which is, in turn, connected to a storage bottle and a vacuum source. When a vacuum is applied to the manifolds through the main pipe, microorganism contained in sample solution in the respective funnels may be caught by the respective membrane filters at the same time.
The above-described and other prior art systems for use in the HGMF filtration usually employ a filter unit comprising a substantially dish-shaped filter holder made of plastic material such as PP(polypropylene) and PE (polyethylene) and a membrane filter detachably mounted to the bottom of the holder. After all the sample solution has passed through the unit, the unit is removed from the system and then the filter is removed from the holder of the unit. The filter carrying microorganism thereon is transferred to a laboratory dish filled with suitable culture medium for cultivation of the microorganism.
With the filter unit of the above-described type, the membrane filter tends to be soon clogged up with food leavings or any other impurities having particle diameter larger than the target microorganism.
A disposable filter unit has also been proposed, in which a membrane filter is fixedly mounted to the bottom of a funnel. In order to provide sufficient liquid-tight abutment between the funnel and the membrane filter, not only the funnel but also the membrane filter should be made of plastic material. Therefore, this filter unit of disposable type is easy to handle but should be too much expensive, which would be a bar to its popularization.
Accordingly, it is a principal object of the present invention to overcome the drawbacks and disadvantages of the prior art membrane filter system for use in the HGMF filtration in bacteriological examination.
Another object of the present invention is to provide a membrane filter unit of unique construction which is easy to handle and inexpensive to manufacture.
To achieve these and other objects, the present invention utilizes a paper funnel that can easily be purchased at a cost much lower than the plastic funnel used in the prior art membrane filter systems. More particularly, the present invention employs a paper funnel with a bottom which may be used as a paper filter. The bottom of the paper funnel will therefore serve as a primary filter to which the sample solution is first subjected before passing through the membrane filter. Microorganism of larger particles in the sample solution should be caught by the primary filter and collected on the bottom of the paper funnel, which eventually prevents clog-up of the membrane filter.
As stated above, the membrane filter unit of the present invention employs the paper funnel in place of the plastic funnel. However, the paper funnel is difficult to be liquid-tightly fitted to the membrane filter because of material difference therebetween. To cope with this problem, in accordance with the present invention, a bottom peripheral flange of the paper funnel is fitted to a ringed groove of a dish-shaped filter holder with resin seal means, to thereby provide liquid-tight engagement therebetween and prevent leakage of the sample solution.
In accordance with an aspect of the present invention, therefore, there is provided a membrane filter system comprising: an integral plastic holder having a filter receiving section, a funnel mount positioned at a level higher than the filter receiving section, and a drainage communicated with the filter receiving section; a membrane filter received in the filter receiving section for collecting target microorganism contained in sample solution; a cup-shaped paper funnel adapted to receive the sample solution, having a bottom sheet and a bottom peripheral flange surrounding the bottom sheet; and resin seal means fitted to the funnel mount to provide liquid-tight engagement between the funnel and the holder, wherein the bottom sheet of the funnel being positioned above the membrane filter, when the funnel is fitted to the funnel mount of the holder, to serve as a primary filter for collecting particles in the sample solution larger than the target microorganism before the sample solution reaches the membrane filter.
In this system, the filter receiving section preferably has a recess for receiving a sheet of porous material which supports thereon the membrane filter. The recess is preferably provided with a plurality of spaced projections for supporting thereon the porous material sheet. A preferable example of the porous material sheet is polypropylene or paper filter.
In one embodiment of the membrane filter system of the present invention, there is a double-wall construction at an upper peripheral portion of a plastic holder. The double-wall construction comprises an inner wall, an outer wall and a groove defined between the inner and outer walls. A bottom peripheral flange of a paper funnel is inserted into the groove which has been filled with liquid silicone resin or any suitable resin material, so that the funnel is liquid-tightly fitted to the holder when resin is hardened. This provides liquid-tight engagement between the paper funnel and the resin holder and prevents leakage of the sample solution to the outside of the system. This membrane filter system is manufactured as a disposable unit.
Accordingly, in accordance with another aspect of the present invention, there is provided a membrane filter system comprising: an integral plastic holder having a filter receiving section, a double-wall construction at an upper peripheral portion of the holder, including an inner wall, an outer wall and a groove defined between the inner and outer walls, a recess formed in the filter receiving section, and a drainage communicated with the recess; a membrane filter received in the filter receiving section for collecting target microorganism contained in sample solution; a cup-haped paper funnel adapted to receive the sample solution, having a bottom sheet and a bottom peripheral flange surrounding the bottom sheet; sealer material poured into the groove of the double-wall construction of the holder and hardened after the bottom peripheral flange of the funnel is inserted into the groove whereby the funnel is liquid-tightly fitted to the funnel; and a sheet of porous material received in the recess of the holder; wherein the bottom sheet of the funnel is positioned above the membrane filter, when the funnel is secured to the funnel by the hardened sealer material, to serve as a primary filter for collecting particles in the sample solution larger than the target microorganism before the sample solution reaches the membrane filter.
In this system, preferably, the holder has a ringed packing member fitted within the filter receiving section to hold down the membrane filter. The membrane filter may be in advance bonded to a bottom of the packing member into a filter unit, which is mounted onto the filter receiving section. A preferable sealer material to be poured into the groove of the double-wall construction of the holder is silicone resin.
In another embodiment of the membrane filter system of the present invention, an integrally formed plastic seal ring is used. A bottom peripheral flange of a paper funnel is fitted to the seal ring which is, in turn, fitted to a housing. This also provides liquid-tight engagement between the paper funnel and the resin holder and prevents leakage of the sample solution to the outside of the system. With this system, the seal ring is detachable with respect to the paper funnel, as well as to the holder.
Accordingly, the seal ring which is relatively expensive and is not directly contaminated by the sample solution during filtering operation is reusable. This reduces the overall costs required for repeat of biological examination.
Accordingly, in accordance with another aspect of the present invention, there is provided a membrane filter system comprising: an integral plastic holder having a filter receiving section, a funnel mount positioned at a level higher than the filter receiving section, a peripheral wall surrounding the funnel mount, and a drainage communicated with the filter receiving section; a membrane filter received in the filter receiving section for collecting target microorganism contained in sample solution; a cup-shaped paper funnel adapted to receive the sample solution, having a bottom sheet and a bottom peripheral flange surrounding the bottom sheet; and a seal ring of resin material that liquid-tightly engages the bottom peripheral flange of the funnel and is liquid-tightly mounted on the funnel mount of the holder within the peripheral wall, wherein the bottom sheet of the funnel being positioned above the membrane filter, when the funnel is fitted to the holder, to serve as a primary filter for collecting particles in the sample solution larger than the target microorganism before the sample solution reaches the membrane filter. The seal ring is typically made of silicone rubber.
In this system, the seal ring may be detachable with respect to the funnel, as well as to the holder. In a preferable embodiment, the seal ring has an inward extension that extends toward the filter receiving section for holding down a peripheral portion of the membrane filter received in the filter receiving section.
In another preferable embodiment of this system, the seal ring has a double-wall construction including an inner wall, an outer wall and a groove defined between the inner and outer walls for detachably engaging the bottom peripheral flange of the funnel. The seal ring is fitted to the funnel in a manner that the outer wall is engaged within the peripheral wall of the holder.
The peripheral wall of the holder may have a plurality of spaced, inward projections for engagement with a top of the seal ring. The peripheral wall of the holder may also have an outward projection.
In another preferable embodiment of this system, the membrane filter is superposed on a secondary filter sheet, both being received in the filter receiving section of the holder. The filter receiving section of the holder is may be provided with a plurality of spaced projections for supporting thereon the secondary filter sheet and the membrane filter.